Here's a rather interesting viewpoint on World of Warcraft's MMO genre dominance. Rather than seeing the Blizzard game's dominance as a detriment to new games, EA Mythic's senior designer Josh Drescher suggest that it actually makes developing a new MMO easier.

"If you actually look at the MMO-sphere right now, that is since WoW launched, the vast percentage of MMOs that launched after it have been successful," Drescher explained. "Obviously no one has eclipsed the 10 million subscriber number, but there have been numerous titles that have come out on different platforms and multiple genres all over the world that have been far more successful than MMOs had been previously."

It's an amazing bit of insight that I hadn't taken into account before. Millions of people are now ready for massively multiplayer games, whereas before World of Warcraft the market was a great deal smaller. While WoW still controls a massive chunk of the market, it's a bigger market than ever before. My girlfriend, who was never much of a gamer before WoW is now looking at Age of Conan and Lord of the Rings Online...living proof of the point.
EA Mythic: WoW has made it easier to develop MMOs
[GamesIndustry.biz]